I think you're not meant to put soap pucks in either of the scuttles or leave them there. The Moss scuttle, the smaller one in the picture, is (at least originally) meant to just keep your lather warm. So you'd get your soap or cream, make lather in a lathering bowl or similar, and then scoop over the lather and rest the lather and brush in the top bowl where it will be kept warm.

Oscar's scuttles, that's the large one in the picture, is similar but is large enough to use as a lathering bowl. So you'd load your brush with soap and/or cream make lather in the scuttle and then just leave it there.